Epoxy resins have been commonly used in the past as encapsulants for light emitting diode (LED) elements and semiconductor chips, from the viewpoint of adhesion with the substrates on which such parts are mounted, as well as toughness and gas barrier properties.
When epoxy resins are used as encapsulants, however, the thermal resistance and light resistance of such resins being inadequate, coloration of the encapsulant is observed with blue and white LEDs that have high heat release and light energy, and thus the performance of such LED elements is significantly reduced.
Much research is therefore being conducted on the use of silicone resins with excellent thermal resistance and light resistance, as LED encapsulants (see Patent Documents 1 and 2, for example). However, since silicone resins have poor adhesion to metal surfaces of wiring sections and with organic resins that are used as reflector plates (reflectors), detachment of encapsulating resins takes place with long-term use when silicone resins are used as LED encapsulating resins.
In order to improve the drawbacks of silicone resins, research has been carried out on epoxysilicone resins that have epoxy groups as substituents in the repeating units of the siloxane backbone (Patent Documents 3 and 4, for example). Such resins are anticipated to exhibit the thermal resistance, light resistance and transparency of silicone resins, in combination with the hardness, strength and adhesion of epoxy resins.
Patent Document 3 discloses a silicone composition comprising an epoxy group and an alicyclic hydrocarbon group as substituents on silicon, and the method accomplishes synthesis by introduction of substituents by hydrosilylation in a siloxane copolymer comprising Si—H groups. Since this method results in unreacted Si—H groups remaining in the composition in many cases, gas bubbles can potentially be included in the cured product due to hydrogen gas generated by hydrolysis of the Si—H groups.
Patent Document 4 discloses a method for producing a polyfunctional epoxysilicone resin wherein a trialkoxysilane compound comprising a glycidyl group or an epoxycyclohexyl group is subjected to high molecularization with water and an acidic catalyst or basic catalyst, and then a monoalkoxysilane is used as an end-capping agent for end capping of the residual alkoxy and silanol groups. While a curable resin composition with high transparency, high hardness, high light resistance and a low shrinkage rate can be obtained by this method, the low proportion of silicone sites in the resin composition can result in thermal resistance problems that are drawbacks of the epoxy resin.
Another problem faced with silicone resins in recent years is high gas permeability. The resulting problems that are encountered include deterioration of inorganic phosphors in LEDs due to moisture passing through the encapsulating resin, and oxidative degradation of the silver plating surfaces of substrate wirings due to oxygen. In this regard, Patent Documents 3 and 4 describe improving thermal resistance, light resistance, transparency, hardness and shrinkage rate by using the resins set forth therein, but they do not mention improvement in gas barrier properties.
Patent Document 5 also discloses a novel epoxy compound useful as a raw material for encapsulants, molding materials, casting materials, laminating materials, composite materials, adhesives and powder coatings for electric, electronic and optical parts, as well as silane coupling agents and modified silicone. However, it does not mention epoxysilicone condensates of the aforementioned epoxy compounds.